In addition to becoming embroiled in numerous ethical scandals, Pruitt has for months provoked the ire of Iowa leaders by falling on the wrong side of the Renewable Fuel Standard, a federal mandate that requires ethanol and biodiesel to be blended into the nation's fuel supply.

"Scott Pruitt’s departure is long overdue," U.S. Rep. David Young, R-Van Meter, said in a statement. "His actions as EPA administrator not only raised serious ethical concerns, but hurt Iowa farmers by recklessly undercutting of the Renewable Fuel Standard. It is my hope that Acting Administrator Andrew Wheeler will uphold the President's commitment to the RFS and get the EPA back on track."

...on Monday assume duties as the acting Administrator of the EPA. I have no doubt that Andy will continue on with our great and lasting EPA agenda. We have made tremendous progress and the future of the EPA is very bright!

President Donald Trump tweeted Thursday afternoon that Pruitt had submitted his resignation. He did not criticize Pruitt, tweeting that, "Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this."

Among the ethical complaints against Pruitt were claims that he relied on aids to run personal errands; approving large raises for some staffers even after the White House had rejected them; allegedly asking that the president fire Attorney General Jeff Sessions and instead appoint him to run the Justice Department; and deleting records of unflattering business meetings from his official calendar.

But his bigger sin, at least in Iowa, was a lack of support for the RFS and Iowa's ethanol industry. Iowa is the nation's largest ethanol and biodiesel producer.

"Administrator Pruitt’s ethical scandals and his undermining of the President’s commitment to biofuels and Midwest farmers were distracting from the agency’s otherwise strong progress to free the nation of burdensome and harmful government regulations," Grassley said in a statement. "Fewer things are more important for government officials than maintaining public trust. Administrator Pruitt, through his own actions, lost that trust."

Iowa's Republican leaders have declined to extend their criticism of Pruitt's policies to Trump, arguing that the former EPA administrator was undermining the president's support of farmers and the RFS.

"Today’s resignation from Administrator Pruitt must result in new EPA leadership that will honor the president’s commitment to the Renewable Fuel Standard," Gov. Kim Reynolds said in a statement. "I will continue to fight for a robust Renewable Fuel Standard by working with our federal delegation in Washington, D.C., to hold the administration to this promise. Iowa farmers deserve nothing less."

Sen. Joni Ernst, recently said Pruitt "is about as swampy as you get here in Washington, D.C., and if the president wants to drain the swamp, he needs to take a look at his own cabinet."